This disclosure relates to a system and method for implementing a hybrid scheme of DL Link adaptation by a Base Station in a Wireless Metropolitan Area Network (WiMAX) described in the IEEE 802.16 specification.
In a WiMAX communications network, a base station (BS) may communicate with a mobile station (MS) on a communication channel. Various factors such as the existence of ambient interference around the MS or BS, movement of the MS, system level performance of the BS, and/or other factors may degrade or otherwise alter the condition of the communication channel. As such, various channel information may be used to indicate the channel condition. There exists a variety of channel information such as, for example, a Physical Carrier to Interference plus Noise Ratio (PCINR), an Effective Carrier to Interference Noise Ratio (ECINR), channel correlation (Corr), Rank, a Received Signal Strength Indicator (RSSI), a Burst Error Rate (BuER) based on an ACK/NACK ratio that indicates a proportion of successful data transmissions to unsuccessful transmission (thereby indicating channel stability), PCINR Standard Deviation that may indicate Doppler and fading effects that result from movement of the MS, system loads, and/or other indicators.
In order to respond to changes to the communication channel, the BS may use different mode configurations. Mode configurations may include, among other things, a Modulation Coding Scheme (MCS) level selection, a Multiple-Input-Multiple-Output (MIMO) mode selection, and/or other mode configurations.
In existing systems, the BS generates a mode configuration that the BS has determined to be suitable. The BS-derived mode configuration may be used in these existing systems irrespective of information available to the MS that may be unavailable to the BS. For example, the BS may use PCINR for Download (DL) link adaptation. However, because PCINR is generated before MIMO decoding by the MS, PCINR may be less accurate than ECINR, which is generated by the MS after MIMO decoding. Thus, the BS may use information for DL link adaptation that may be less accurate than information available to the MS. In other existing systems, the MS may generate a recommended mode configuration that the MS has determined to be suitable. In these existing systems, the MS mode recommendation may be used irrespective of information available to the BS that may be unavailable to the MS. The MS 106 mode recommendation and the BS-derived mode configuration may be different because MS 106 and BS 110 disagree on the channel condition. If such disagreement is sufficiently high, then confidence that either is correct may be reduced. Thus, selecting one or the other may result in a selection of an inappropriate mode configuration because the MS, the BS, or both may be incorrect when determining the channel condition.
Thus, by using either an exclusive BS-centric or exclusive MS-centric approach for DL link adaptation, existing systems may not adequately make an appropriate decision because in some instances the BS may have better information applicable for DL link adaptation than the MS while in other instances the MS may have better information applicable to the mode decision than the BS. Vendors currently widely ignore the MS-derived recommendation because they often believe that the MS recommendation may not be as reliable as the BS recommendation.
These and other drawbacks exist.